Candida albicans is the leading cause of oral candidiasis worldwide. The ability to undergo a reversible transition from yeast (ovoid, budding cells) to hyphal filaments (elongated cells attached end-to-end) is a key virulence trait that allows C. albicans to be a successful opportunistic pathogen. The transition to filaments is co-regulated with other virulence factors and occurs in response to several host environmental conditions including 370C, serum, carbon/nitrogen starvation and neutral pH. Exposure to these growth conditions activates numerous signal transduction pathways that promote virulence-related gene expression and hyphal growth, but little is known about the mechanisms that control the expression and activity of filament-specific transcription factors. Although antifungal therapies are available to treat candidiasis, many antifungal drugs have adverse side effects and are fungistatic, not fungicidal. The long term goal of our studies is to gain insight into morphogenesis to identify novel antifungal drug targets. Our objective is to understand how C. albicans regulators of filamentation respond to environmental stimuli via transcriptional and posttranslational mechanisms. Our studies will focus on Ume6, Nrg1 and Rfg1, key transcription factors that regulate hyphal- specific gene expression and filamentation. We hypothesize that environmental filament-inducing conditions differentially control the transcriptional regulation and activity of Ume6, Nrg1 and Rfg1. We propose the following Specific Aims to address our hypothesis: Specific Aim 1: Determine the mechanism(s) by which UME6 and NRG1 are transcriptionally regulated in response to environmental filament-inducing conditions. Specific Aim 2: Determine the transcriptional activity of Ume6, Nrg1 and Rfg1 in response to several environmental conditions. In order to address Aim 1, we will use a promoter deletion analysis with a lacZ reporter assay, electrophoretic mobility shift assays and mass spectrometry to identify the transcriptional regulators that control NRG1 and UME6 expression in response to specific environmental stimuli. To address Aim 2, we will use a one-hybrid system with a lacZ reporter gene to investigate the transcriptional activity of Ume6, Nrg1 and Rfg1 in response to environmental conditions. We will use RT-qPCR in both Aims to quantify lacZ expression. At the completion of our studies, we expect to have a better understanding of the environmental regulation of C. albicans morphogenesis, which will aid in the development of new antifungal therapies. PUBLIC HEALTH RELEVANCE: Candida albicans is the leading cause of oral fungal infections worldwide due, in part, to the global HIV pandemic. Our studies will provide insight into a key virulence factor, the ability to switch between yeast and filamentous forms, which makes this organism a successful opportunistic pathogen. This knowledge will aid in the development of new antifungal therapies.